Detoxifying agent for use in disposal of noxious wastes that is conducted by solidifying them with cement

ABSTRACT

A detoxifying agent for use in disposal of noxious wastes that is conducted by solidifying them with cement, consisting essentially of an aqueous solution which comprises as main components (a) small-sized metal cations whose 6-coordination ionic radii are less than 100 pm, (b) medium-sized metal cations whose 6-coordination ionic radii are between 100 pm and 140 pm, and (c) large-sized metal cations whose 6-coordination ionic radii are in excess of 140 pm. This detoxifying agent can provide cement-solidified materials having high strength, substantially free from exudation of toxic substances such as heavy metals, PCBs and dioxins.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a detoxifying agent that is used whennoxious wastes are treated with cement to solidify them. Moreparticularly, the present invention relates to a detoxifying agent foruse in disposal of noxious wastes, capable of providingcement-solidified materials having high strength, substantially freefrom exudation of toxic substances such as heavy metals, PCBs anddioxins.

2. Background Art

How to finally dispose of noxious wastes such as residues from theincineration of refuse, component (especially, molten slag and heavymetals) from the incineration of hazardous industrial wastes, pollutedsoil, river sludge, sewage sludge, waste glass and waste tires is now aserious social problem. These noxious wastes can discharge a variety oftoxic substances, and, of these toxic substances, heavy metals, PCBs,dioxins, etc., in particular, are known to exert serious effects onecosystem. For this reason, there has been strongly demanded a techniqueof finally disposing of noxious wastes without discharging the abovetoxic substances.

To meet the above demand, there have been proposed various methods formaking noxious wastes innoxious, and subjecting them to recycling. Oneof these methods proposed is as follows: noxious waste containing theabove-described toxic substances is mixed with cement, and the mixtureis solidified to enclose the toxic substances in the cement; thecement-solidified material thus obtained is then subjected to recycling.However, the toxic substances tend to inhibit the agglomeration ofcements, so that they retard the hardening of cement, and impartdecreased strength to the cement-solidified material. Another problem isthat the toxic substances enclosed in cement can ooze out of thecement-solidified material.

To solve these problems, the following method has been proposed asdisclosed in Japanese Patent Laid-Open Publication No. 24276/1998: asolution containing, as main components, tannin and wood vinegar isdiluted with water, and this aqueous solution is added as a detoxifyingagent to noxious waste containing such toxic substances as heavy metalsand PCBs to detoxify them. It is considered that, since tannin and woodvinegar exert a powerful chelating action on elemental compounds such asheavy metals, the detoxification of heavy metals and the like cansuccessfully be attained by this method. However, althoughcement-solidified materials obtained by this method show strength tosome degree, a further improvement in the strength has been expected.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a detoxifying agentthat is used when noxious wastes are treated with cement to solidifythem, and that can provide cement-solidified materials having highstrength, substantially free from exudation of toxic substances such asheavy metals, PCBS and dioxins.

The present invention provides a detoxifying agent for use in disposalof noxious wastes that is conducted by solidifying them with cement,consisting essentially of an aqueous solution which comprises as maincomponents (a) small-sized metal cations whose 6-coordination ion radiiare less than 100 pm, (b) medium-sized metal cations whose6-coordination ionic radii are between 100 pm and 140 pm, and (c)large-sized metal cations whose 6-coordination ionic radii are in excessof 140 pm. The present invention also provides cement-solidifiedmaterials that can be obtained through the use of the above-describeddetoxifying agent.

DETAILED DESCRIPTION OF THE INVENTION

The detoxifying agent according to the present invention, for use indisposal of noxious wastes that is conducted by solidifying them withcement will be described hereinafter.

Detoxifying Agent

In the present invention, the “detoxifying agent” is an additive that isused when noxious wastes are treated with cement to solidify them. Thepurposes of this agent are to detoxify toxic substances contained innoxious wastes, thereby enclosing the detoxified substances in cementwithout discharging them, and to prevent toxic substances from exertingtheir effect of inhibiting the setting of cement, thereby obtainingcement-solidified materials having increased strength.

In the present invention, the “treatment with cement for solidification”is conducted for the purpose of disposing of noxious wastes. Thistreatment is useful in enclosing, in cement, such toxic substances asheavy metals, PCBs and dioxins contained in noxious wastes, therebyobtaining recyclable cement-solidified materials.

The “noxious wastes” that can be disposed of by the present inventioninclude a variety of wastes that can discharge toxic substances such asheavy metals, dioxins and PCBs, and there is no particular limitation onthem. Examples of such noxious wastes include residues from theincineration of refuse, component (especially, molten slag and heavymetals) from the incineration of hazardous industrial wastes, pollutedsoil, river sludge, and sewage sludge. In addition, waste glass, tires,plastics and CD, and the like are also included in the noxious wastes.

As mentioned previously, even if the above-described noxious wastes aretreated with cement and solidified, toxic substances enclosed in thecement can ooze out of the cement-solidified materials. Moreover, sincethe toxic substances have the effect of inhibiting the setting ofcement, the hardening of cement is retarded, and the resultingcement-solidified materials are to have decreased strength.

We found that it is possible to make the degree of exudation of toxicsubstances extremely low, and, at the same time, to obtaincement-solidified materials having increased strength if a detoxifyingagent having a specific composition is used when noxious wastes aretreated with cement to solidify them.

A detoxifying agent according to the present invention consistsessentially of an aqueous solution comprising as main components (a)small-sized metal cations whose 6-coordination ionic radii are less than100 pm, (b) medium-sized metal cations whose 6-coordination ionic radiiare from 100 to 140 pm, and (c) large-sized metal cations whose6-coordination ionic radii are more than 140 pm.

The “6-coordination ionic radii” herein mean ionic radii where thecoordination number is 6, and refer to the generally known values thatwere determined by Shannon and Prewitt on the basis of observed values,and improved by Shannon. These ion radii (CR: crystal ionic radii) areenumerated on pages 725-726 of “Kaitei Yon-han, Kagaku Binran, Kiso-henII (Handbook of Chemistry, Basic Section II, Fourth Revised Edition)”,edited by The Chemical Society of Japan, published by Maruzen Co., Ltd.,Japan.

The 6-coordination ionic radii of major ions useful for the presentinvention are as follows:

(a) as small-sized metal cations: Li⁺: 90 pm, Mg²⁺: 86 pm, Mn²⁺: 81 pm,97 pm, Fe³⁺: 69 pm, 79 pm, Ni²⁺: 83 pm;

(b) as medium-sized metal cations: Na⁺: 116 pm, Ca²⁺: 114 pm, Sr²⁺: 132pm; and

(c) as large-sized metal cations: Ba²⁺: 149 pm, K⁺: 152 pm, Rb⁺: 166 pm.

In addition, examples of halide anions include Cl⁻ and Br⁻, and theirionic radii are 167 pm and 182 pm, respectively. Regarding theabove-described ionic radii of Mn²⁺ and Fe³⁺, the former value shows theradius of the ion that is in the low spin state, and the latter oneshows the radius of the ion that is in the high spin state.

It is considered that, since metal cations selected from each of thethree groups of ions that are different in the range of ionic radii areincorporated into the detoxifying agent of the present invention, thedetoxifying agent can exert various detoxifying actions, such as acoagulating effect, on a wide variety of toxic substances. In thesolidification of noxious wastes with cement, various toxic substancesare considered to exist, and even if only a few of these toxicsubstances have the effect of inhibiting the setting of cement, it isunavoidable that the hardening of cement is adversely effected.Therefore, to incorporate, into the detoxifying agent, metal cationsselected from each of the above-described groups (a), (b) and (c), whichare different in the range of ionic radii, is considered to be quiteeffective in making the detoxifying agent useful for the detoxificationof a wide variety of toxic substances.

(a) Small-Sized Metal Cations

Small-sized metal cations for use in the present invention are metalcations whose 6-coordination ionic radii are less than 100 pm.Preferably, the small-sized metal cations include at least one ionselected from alkali metal ions, alkaline-earth metal ions and 3dtransition metal ions. More preferably, the metal cations include ionsselected from each one of these three groups. It is considered that,since two or more different types of ions are thus allowed to exist inthe detoxifying agent, a wider variety of toxic substances can bedetoxified. The “3d transition metals” herein refer to the transitionmetals with atomic numbers of 21 (Sc) to 29 (Cu), having an unfilled 3dshell; this transition metal series is also called the elements of thefirst transition series.

There is no particular limitation on the small-sized metal cations foruse in the present invention. Preferable examples of the metal cationsinclude Li⁺, Mg²⁺, Mn²⁺, Fe³⁺ and Ni²⁺, and it is most preferable to useall of these ions as the small-sized metal cations. It is preferablethat these metal cations be supplied to the aqueous solution in the formof halides. It is more preferable that the metal cations such besupplied to the aqueous solution in the form of, for instance, lithiumchloride, magnesiumchloride, manganese (II) chloride, iron (III)chloride, and nickel (II) chloride. This is because, since these halidesare strong electrolytes, they are completely ionized in the solution.

(b) Medium-Sized Metal Cations

Metal cations of any type can be used as the medium-sized metal cationsfor use in the present invention as long as their ionic radii fall inthe range of 100 to 140 pm. The medium-sized metal cations preferablyinclude at least one ion selected from alkali metal ions andalkaline-earth metal ions, more preferably ions selected from both ofthese two groups. It is considered that, since two or more types of ionsare thus allowed to exist in the detoxifying agent, the detoxificationof a wider variety of toxic substances can successfully be attained.

Specific examples of the medium-sized metal cations that can preferablybe used in the present invention include Na⁺, Ca²⁺ and Sr²⁺, and it ismost preferable to use all of these ions. It is preferable that thesemetal cations such be supplied to the aqueous solution in the form ofhalides. It is more preferable that the metal cations such be suppliedto the aqueous solution in the form of, for example, sodium chloride,calcium chloride and strontium chloride. This is because, since thesehalides are strong electrolytes, they are completely ionized in thesolution.

(c) Large-Sized Metal Cations

The large-sized metal cations for use in the present invention are thoseones whose ionic radii are greater than 140 pm. Preferably, thelarge-sized metal cations include at least one ion selected from alkalimetal ions and alkaline-earth metal ions. More preferably, the metalcations include ions selected from both of these two groups. It isconsidered that, since two or more types of ions are thus allowed toexist in the detoxifying agent, a wider variety of toxic substances cansuccessfully be detoxified.

Specific examples of the large-sized metal cations that can preferablybe used in the present invention include Ba²⁺, K⁺ and Rb⁺, and it ismost preferable to use all of these ions. It is preferable that thesemetal cations such be supplied to the aqueous solution in the form ofhalides. It is more preferable that the metal cations in the form of,for example, barium bromide, potassium chloride and rubidium chloride besupplied to the aqueous solution. This is because, since these halidesare strong electrolytes, they are completely ionized in the solution.

In the detoxifying agent of the present invention, it is preferable touse, as the metal cations, alkali metal ions, alkaline-earth metal ionsand 3d transition metal ions as described hereinbefore. The reason whyions of these three types are used is that these ions are geochemicallyimportant and stable in any environment over a long period of time.Alkali metal ions have strong salting-out power (show high bond strengthwith water), and tend to coagulate colloidal toxic substances, so thatthey are considered to act to detoxify toxic substances. Alkaline-earthmetal ions form sparingly soluble salts, and have solidifying, hardeningand adhering effects. They are therefore considered to act to detoxifytoxic substances. 3d Transition metal ions form sparingly soluble saltsor complexing salts, so that they are considered to have the effect ofdetoxifying toxic substances.

The detoxifying agent of the present invention thus comprises a varietyof metal cations including ions whose ionic radii fall in at least threedifferent ranges, the ions being preferably selected from each one ofthe three groups of alkali metal ions, alkaline-earth metal ions and 3dtransition metal ions. The detoxifying agent of the invention cantherefore harmoniously exert, on a variety of toxic substances, sucheffects as coagulating, dehydrating and complexing effects, and theeffect of forming sparingly soluble compounds (precipitates). It isconsidered that, since these effects are synergistically exerted onvarious toxic substances, the toxic substances are detoxified moreefficiently and completely.

Optional Components

In the present invention, various optional components may beincorporated into the detoxifying agent as needed within the scope ofthe invention.

It is noted that, since such components as tannin and wood vinegar caninhibit the hardening of cement as can be known from the resultsobtained in Example 2 and Comparative Example 2, it is desirable toincorporate substantially no tannin and wood vinegar into thedetoxifying agent of the present invention.

Properties of Solution

There is no particular limitation on the condensation of each of theabove-described metal ions in the detoxifying agent of the presentinvention, or on the ionic strength of the detoxifying agent. These twoproperties may be properly decided depending on the waste to be disposedof, or on the manner in which the detoxifying agent is used.

According to a preferred embodiment of the present invention, thedetoxifying agent is prepared so that it will have an ionic strength ofpreferably 1 or more, more preferably 2 to 4. The detoxifying agent canmore efficiently exert various effects such as a coagulating effect ontoxic substances as long as it has an ionic strength in the above range.

According to a preferred embodiment of the present invention, thedetoxifying agent is prepared so that its pH will fall in the range of 6to 8. The detoxifying agent of the present invention having such a pH isadvantageous in that it is nearly harmless to human body, is easy forhandling and preservation, and can be a stable aqueous solution.

Preparation Method

The detoxifying agent of the present invention may be prepared by amethod that is selected properly depending upon the types of componentsto be used, and there is no particular limitation on the productionmethod. For example, in the case where alkali metal ions, alkaline-earthmetal ions and 3d transition metal ions are used, the following methodmay be employed. Halides of alkali metals are firstly placed in a firstvessel, while halides of alkaline-earth metals and those of 3dtransition metals are placed in a second vessel. Hot water at about 90°C. or higher is poured into these vessels so that the ratio by volume ofthe quantity of the hot water in the first vessel to that of the hotwater in the second vessel will be from 6:4 to 8:2, followed bystirring. The aqueous solution in the first vessel and that in thesecond vessel are then mixed. This mixture is stirred again, and cooledto room temperature to give a detoxifying agent of the presentinvention.

Usage

The detoxifying agent of the present invention is mixed with noxiouswaste to be disposed of, water and cement, and there is no particularlimitation on the order of mixing.

According to a preferred embodiment of the present invention, thedetoxifying agent is used in the following manner. After adding thedetoxifying agent to noxious waste and agitating the mixture, cement isadded to this mixture, and the resultant mixture is further agitated; aproper amount of water is then added to this mixture, and the mixtureobtained is thoroughly agitated. When the detoxifying agent is used inthis manner, the effects of the present invention can be obtained moreefficiently.

Any type of cement including Portland cement, Portland blast furnaceslag cement and fly ash cement can be used together with the detoxifyingagent of the present invention. It is however preferable to use ordinaryPortland cement since this cement shows sufficiently high initialstrength, is economically advantageous, and is effective in obtainingcement-solidified materials that are stable in quality.

The detoxifying agent of the present invention is considered to functionin the following way. The detoxifying agent exhibits its various effectsas the hydration reaction of cement proceeds, and needle crystals arethus produced in pores of various sizes formed in the hardened cement.These needle crystals are crystals having no water unlike simplehydrates of cement, so that the hardened cement is to have a denserconstitution. It is considered that, owing to this denser constitution,the hardened cement shows increased strength and durability, and becomesslow to undergo corrosion.

Cement-Solidified Material

The cement-solidified material obtained through the use of thedetoxifying agent of the present invention is such that toxic substancescontained in noxious waste have efficiently been detoxified due to thevarious effects of the detoxifying agent, such as the effect of formingsparingly soluble compounds (precipitates), and coagulating, hydratingand complexing effects. Therefore, the cement-solidified material exudessubstantially no toxic substances, and is excellent in both strength anddurability.

It is preferable to reuse the cement-solidified materials as durablematerials. Preferable examples of durable materials include secondaryproducts of concrete such as interlocks, flat plates, concrete curbs,car stops, and tetrapod. Thus, it becomes possible to recycle noxiouswastes efficiently and safely.

EXAMPLES

The detoxifying agent of the present invention will now be explainedmore specifically by referring to the following examples. However, theseexamples are not intended to limit or restrict the scope of the presentinvention in any way.

Example 1 & Comparative Example 1

Cement-solidified materials were produced by using and without using adetoxifying agent of the present invention, and compared with each otherin terms of compressive strength and the degree of exudation of toxicsubstances.

Example l

A detoxifying agent of the present invention was prepared by using thefollowing compounds.

(A) Halides of alkali metals: Sodium chloride  60 g Potassium chloride 30 g Rubidium chloride  10 g (B) Halides of alkaline earth metals:Magnesium chloride  15 g Calcium chloride  10 g Strontium chloride 7.5 gBarium bromide   3 g (C) Halides of 3d transition metals Manganese (II)chloride 1.5 g Iron (III) chloride 1.5 g Nickel (II) chloride   5 g

The above-listed halides of alkali metals (A) were placed in a vessel I,and the halides of alkaline earth metals (B) and those of 3d transitionmetal elements (C) were placed in a vessel II. Hot water at about 90° C.or higher was poured into the vessel I in an amount of 700 ml, and intothe vessel II in an amount of 300 ml, and the mixture in each vessel wasstirred quickly. The mixture in the vessel I and that in the vessel IIwere transferred to an other vessel III at the same time, and themixture obtained was stirred again. This mixture was cooled in the airat room temperatures to give a detoxifying agent of the presentinvention.

Six parts by volume of the above-prepared detoxifying agent was added to40 parts by volume of river sludge. To this mixture was added 30 partsby volume of river sand as fine aggregate, and the mixture obtained wasagitated quickly. 30parts by volume of Portland cement and a properamount of water were further added to the above mixture, and the mixturewas agitated again. Samples for use in the following tests were made inthis manner.

After the cement was hardened, the samples were cured for 7 days and for28 days in the wet air, and a compressive strength test was conducted inaccordance with JIS A5201 (Physical Testing Methods of Cement, 1992).The results are shown in Table 1.

In addition, after curing the above-obtained sample for 28 days in theair, an exudation test was carried out in accordance with NotificationNo.13 of the Environment Agency, Japan to measure the concentrations oftoxic heavy metals in a liquid exuded from the sample. For reference,the concentrations of toxic heavy metals in the river sludge itself(original sludge) were also measured. The results are shown in Table 2.

Comparative Example 1

River sludge was solidified with cement in the same manner as in Example1 except that the detoxifying agent of the present invention was notadded, and the samples obtained were subjected to the same compressivestrength test as in Example 1. The results are shown in Table 1.

TABLE 1 Compressive Strength (kgf/cm²) After 7 days After 28 daysExample 1 45.0 51.44 Comparative Example 1  9.7 31.17

TABLE 2 Concentration in Concentration in Liquid Toxic Original SludgeExuded from Cement- Subtance (mg/kg) Solidified Material (mg/l) Cadmium8.5 less than 0.01 Lead 292 0.01 Chromium (VI) less than less than 20.05 Arsenic 87.7 less than 0.01 PCB less than less than 0.01 0.0005

The data shown in Tables 1 and 2 demonstrate the following: In the casewhere the detoxifying agent of the present invention is used when riversludge containing organic impurities is solidified with cement, theresulting cement-solidified material shows sufficiently high compressivestrength. With respect to the exudation of toxic substances, onlyextremely small amounts of toxic substances are found to have exudedfrom the cement-solidified material, so that it is confirmed that thecement-solidified material is substantially free from exudation of toxicsubstances. Further, the concentrations of the toxic substances in theliquid exuded from the cement-solidified material fulfil the criteriaset for the disposal of industrial wastes.

Example 2, Comparative Examples 2 & 3

Cement-solidified materials were produced by using the detoxifying agentof the present invention, by using a conventional detoxifying agent, andwithout using any detoxifying agent, and subjected to a strength test.

Example 2

Water, cement (ordinary Portland cement), fine aggregate (land sand fromFuttsu, Chiba-ken, Japan), and the detoxifying agent prepared in Example1 were mixed in accordance with the formulation shown in Table 3. Thiscement mixture was cured in the air under the conditions of 28° C. and78 RH %. 7, 14and28days after the mixing, the compressive strength ofthe cement mixture was measured by the same method as in Example 1. Theresults are shown in Table 3.

Comparative Example 2

A cement mixture was prepared in accordance with the formulation shownin Table 3 in the same manner as in Example 2. It is noted that thedetoxifying agent used in this example is a conventional agentcontaining tannin and wood vinegar as its main components. This cementmixture was cured, and then subjected to the measurement of compressivestrength in the same manner as in Example 2. The results are shown inTable 3.

Note that the above conventional detoxifying agent is an aqueoussolution prepared by dissolving the following compounds in one litter ofhot water.

Tannin 2 g Wood vinegar 3 g Sodium chloride 83.3 g Potassium chloride125.3 g Potassium bromide 9 g Lithium chloride 2.4 g Barium chloride 18g Calcium sulfate 12 g Magnesium chloride 12 g Strontium chloride 6 gCobalt chloride 12 g Copper chloride 6 g Zinc chloride 6 g

Comparative Example 3

A cement mixture was prepared in accordance with the formulation shownin Table 3 in the same manner as in Example 2. It is noted that anydetoxifying agent was not used in this example. This cement mixture wascured, and then subjected to the measurement of compressive strength inthe same manner as in Example 2. The results are shown in Table 3.

TABLE 3 Example Comp. Comp. 2 Ex. 2 Ex. 3 Quantity Detoxifying agent60.5 — — Conventional — 67.5 — detoxifying agent Water 284 284 338Cement 520 520 520 Sand 1040 1040 1040 Strength After 7 days 242 178 198After 14 days 287 218 236 After 28 days 388 306 321 *Quantity: (g);Strength: (kgf/cm²)

The data shown in Table 3 demonstrate the following:

(1) The cement mixture prepared by using the detoxifying agent of thepresent invention is superior to the cement mixture prepared by usingthe conventional detoxifying agent in the strength measured after the7-day curing. The cement-solidified material of the present inventioncan therefore be subjected to bulk transportation relatively early afterits production.

(2) The cement mixture prepared by using the detoxifying agent of thepresent invention is largely superior to the cement mixture prepared byusing the conventional detoxifying agent also in the strength measuredafter the 28-day curing. It is therefore considered that thecement-solidified material of the present invention can be used over aprolonged period of time for those applications where high strength isrequired. The reason why the cement mixture prepared by using theconventional detoxifying agent (Comparative Example 2) is, on the whole,inferior in strength to the cement mixture prepared without using anydetoxifying agent (Comparative Example 3) is that tannin and woodvinegar inhibit the hardening of cement.

As mentioned above, when the detoxifying agent according to the presentinvention is used, cement-solidified materials having high strength,substantially free from exudation of toxic substances can be obtained.This means that it becomes possible to prevent environmental pollution,and to effectively reuse noxious wastes as cement-solidified materialswhen the detoxifying agent of the invention is used.

What is claimed is:
 1. A detoxifying agent for use in disposal of noxious wastes that is conducted by solidifying them with cement, consisting essentially of an aqueous solution which comprises as main components: (a) small-sized metal cations whose 6-coordination ionic radii are less than 100 pm, comprising alkaline-earth metal ions and 3d transition metal ions; (b) medium-sized metal cations whose 6-coordination ionic radii are between 100 pm and 140 pm, comprising alkali metal ions and alkaline-earth metal ions; and (c) large-sized metal cations whose 6-coordination ionic radii are in excess of 140 pm, comprising alkali metal ions and alkaline-earth metal ions; and wherein the detoxifying agent comprises substantially no tannin or wood vinegar.
 2. The detoxifying agent according to claim 1, wherein each of the metal cations (a), (b) and (c) includes at least one ion selected from the group consisting of alkali metal ions, alkaline earth metal ions and 3d transition metal ions.
 3. The detoxifying agent according to claim 1, wherein the metal cations (a), (b) and (c) are supplied to the aqueous solution in the form of halides.
 4. The detoxifying agent according to claim 1, having an ionic strength of 1 or more.
 5. The detoxifying agent according to claim 4, having an ionic strength of 2 to
 4. 6. The detoxifying agent according to claim 1, wherein the small-sized metal cations include at least one ion selected from the group consisting of Li⁺, Mg²⁺, Mn²⁺, Fe³⁺ and Ni²⁺.
 7. The detoxifying agent according to claim 6, wherein the small-sized metal cations include all of the ions Li⁺, Mg²⁺, Mn²⁺, Fe³⁺ and Ni²⁺.
 8. The detoxifying agent according to claim 1, wherein the medium-sized metal cations include at least one ion selected from the group consisting of Na⁺, Ca²⁺ and Sr²⁺.
 9. The detoxifying agent according to claim 8, wherein the medium-sized metal cations include all of the ions Na⁺, Ca²⁺ and Sr²⁺.
 10. The detoxifying agent according to claim 1, wherein the large-sized metal cations include at least one ion selected from the group consisting of Ba²⁺, K⁺ and Rb⁺.
 11. The detoxifying agent according to claim 10, wherein the large-sized metal cations include all of the ions Ba²⁺, K⁺ and Rb⁺.
 12. The detoxifying agent according to claim 1, having a pH of 6 to
 8. 13. A cement-solidified material obtained through the use of a detoxifying agent according to claim
 1. 14. The detoxifying agent according to claim 2, wherein the metal cations (a), (b) and (c) are supplied to the aqueous solution in the form of halides.
 15. The detoxifying agent according to claim 2, having an ionic strength of 1 or more.
 16. The detoxifying agent according to claim 3, having an ionic strength of 1 or more.
 17. The detoxifying agent according to claim 1, wherein the small-sized metal cations include alkali metal ions, alkaline-earth metal ions and 3d transition metal ions. 